Such a tank as described above is generally known as a separator tank. The liquid introduced into such a separator tank is typically to be stored therein for the duration of a space experiment or other space mission. The liquid may be a propellant or fuel, or some other liquid, that is supplied to the separator tank from a supply or test tank that is connected upstream to the separator tank. A pressurized propellant or driving gas, typically an inert gas such as helium (He) or nitrogen (N2) gas, is supplied under pressure into the upstream supply tank and serves to pressurize and drive the fluid out of the supply tank through a pipeline system into the separator tank. Thereby, the fluid supplied from the supply tank to the separator tank may comprise a liquid, a gas, or a liquid-gas mixture. Simultaneously, a corresponding quantity of pure gas (without liquid) is driven out of the separator tank, whereby this extracted gas is typically emitted or ejected out of the experimental module into the vacuum of space prevailing at the orbit of the experimental module. If a liquid-gas mixture escapes from the separator tank and is emitted or ejected out into the vacuum of space, this leads to a varying density of the ejected fluid, i.e. a varying density of the ejected liquid and gas depending on the mixture ratio of the two phases, which in turn causes an inconstant or varying thrust profile. For this reason, such ejection of a liquid-gas mixture is undesirable and is to be avoided. Particularly, it is desired to ensure that only pure gas is output from the separator tank.
The following processes are known and utilized in the field of space travel technology for achieving a sure and reliable separation of the liquid phase from the gas phase. First, by heating the propellant or other liquid-gas mixture coming from the supply tank, thereby the liquid in such a mixture is vaporized into the gas phase. However, this process requires a relatively high expenditure of energy for heating and vaporizing the liquid. A second known procedure involves applying an additional acceleration or settling thrust to cause the liquid propellant to settle at a portion of the tank away from the gas outlet, so that at the time of the pressure release or gas extraction from the tank, no liquid is located at or near the tank outlet. This, however, requires a precisely directed and metered acceleration by means of an additional thruster or other drive system, which is excluded in the case of a weightless experiment though, because it would impair the boundary conditions of the experiment.
Additionally, the U.S. Pat. No. 4,027,494 discloses the use of phase separators for separating a liquid from a gaseous phase, in an apparatus with a phase separator for operating conditions with small acceleration, and the separation of gas from liquid is carried out using superconducting magnets. Furthermore, U.S. Pat. No. 4,848,987 discloses a phase separator in which pumps and a series of valves are provided to achieve the separation. Also, U.S. Pat. No. 7,077,885 discloses a phase separator that uses a propeller to impose a rotation on the liquid-gas mixture, and includes a membrane of polyethylene or nylon by which the liquid, in this case water, is separated from the gas. The latter known system is provided for use in an application with fuel cells and is not suitable for separating cryogenic liquids. Still further, U.S. Pat. No. 4,435,196 and U.S. Pat. No. 4,617,031 disclose apparatuses for separating a liquid phase from a gas phase in applications limited to use in the gravitational field on earth.
Moreover, U.S. Pat. No. 4,027,494 discloses an arrangement that supplies a pure liquid that has been purified of possible gas inclusions or admixtures. For separating the gas from the liquid, this known arrangement includes a honeycomb-like structure arranged over a liquid outlet, which ensures that no gas can penetrate into the liquid outlet line.
An apparatus disclosed in U.S. Pat. No. 4,435,196 includes a porous bed structure in the form of a per se known catalyst bed for producing gas from a liquid propellant or fuel, for example hydrazine. This patent further discloses a liquid-gas separator comprising a titanium net that aims to restrain or hold back gas bubbles due to the effects of capillary forces and surface tension.
Finally, the German Patent DE 10 2007 005 539 and its counterpart U.S. Pat. No. 8,048,211 disclose an arrangement of the general type initially described above, in which a separator is arranged as a component in a propellant tank, wherein a liquid-gas mixture at various locations in the propellant tank can reach a reservoir provided for storing the liquid.